Linear saturated aliphatic thiol esters as defined throughout this application have the formula: EQU RCH.sub.2 CH.sub.2 COSR'
wherein R is selected from the group consisting of hydrogen and alkyl radicals containing from zero to 28 carbon atoms and R' is selected from the group consisting of alkyl and aryl radicals containing up to 10 carbon atoms, including phenyl (C.sub.6 H.sub.5) and alkylated phenyl wherein the alkyl groups contain from 1 to 4 carbon atoms.
Linear unsaturated aliphatic thiol esters as defined herein have the formula: EQU RCH = CHCOSR'
wherein R and R' have the same definitions defined supra.
The usual preparation of saturated thiol esters is by the reaction or a mercaptan with an acid chloride frequently in the presence of pyridine. Sometimes anhydrides are substituted for the acid chlorides. Other preparations include the reaction of an acid chloride with a metal mercaptide, or the reaction of a thio acid salt and an alkyl halide among other methods. These thiol esters may be treated with amines to form N-substituted carboxamides and a mercaptan or may be desulfurized with fresh Raney nickel to produce an alcohol (i.e. RCOSR' .fwdarw. RCH.sub.2 OH) etc.
It is noteworthy that the synthesis of saturated and unsaturated thiol esters from 1-alkenes or 1-alkynes with "classical" carbonylation catalysts, such as the Reppe nickel carbonyl catalysts, gives mainly branched-chain thiol esters rather than the more desirable linear thiol esters, in moderate yields, and under fairly stringent reaction conditions. For example, the synthesis of ethyl thiol-.alpha.-methyl octanoate in 15% yield from octene*. FNT *W. Reppe and H. Kroper, Ann.
In both types of products, linear saturated and unsaturated thiol esters, the methods of synthesis are not entirely satisfactory, for example yields are poor or erratic, purification is difficult and/or reaction conditions are rigorous, and in many instances predominantly branched-chain rather than linear thiol esters are produced.
In this invention, noble metal catalysts, particularly ligand-stabilized noble-metal halide catalysts, in conjunction with Group IVB metal halide co-catalysts (both types of catalysts to be described subsequently), are used to catalyze the addition of carbon monoxide into the carbon-to-carbon unsaturated bonds of 1-alkenes or 1-alkynes in the presence of a sulfur containing nucleophile having a mobile hydrogen atom, preferably a mercaptan, to produce linear saturated or unsaturated thiol esters. For instance, the synthesis of a typical linear saturated thiol ester, such as ethyl thioloctanoate, is shown below: EQU CH.sub.3 (CH.sub.2).sub.4 CH = CH + CO + C.sub.2 H.sub.5 SH .fwdarw. CH.sub.3 (CH.sub.2).sub.5 CH.sub.2 COSC.sub.2 H.sub.5
Similarly, the preparation of an illustrative unsaturated thiol ester is as follows: EQU HC .tbd. CH + CO + C.sub.3 H.sub.7 SH .fwdarw. H.sub.2 C = CHCOSC.sub.3 H.sub.7
It should be noted that the instant invention is also distinguishable over related co-assigned cases* in that:
1. In the related cases, while the same classes of homogeneous noble metal catalysts are used in conjunction with carbon monoxide and unsaturated substances, sulfurcontaining nucleophilic reactants are employed in this case rather than the oxygen-containing nucleophilics such as alkanols, phenols, and water described in the previous cases. FNT *Ser Nos. 233,014 and 233,015